The manufacture of semiconductor devices, and in particular advanced semiconductor devices with very small feature sizes, higher device density and larger chip sizes requires the use of ultra-high purity (UHP) nitrogen gas as an inerting medium during various semiconductor processing steps. It is not uncommon for large semiconductor fabrication houses (FABS) to require in excess of 100,000 standard cubic feet per hour (SCFH) of UHP nitrogen. The UHP nitrogen is produced by separating the nitrogen from atmospheric air using well-known cryogenic technologies. The cryogenically separated nitrogen is then further treated to remove trace quantities of hydrogen, carbon monoxide, oxygen, carbon dioxide and water.
A number of techniques for removing these unwanted species (hydrogen, carbon monoxide, oxygen, carbon dioxide and water) from nitrogen are known. Several techniques are discussed in the specification of U.S. Pat. No. 4,869,883 which is incorporated herein by reference.
One particularly effective method for removing the unwanted species is by passing the nitrogen gas through a bed of a nickel-based catalytic adsorbent. The known adsorbents are capable of removing parts-per-million (ppm) levels of oxygen, carbon monoxide, hydrogen, carbon dioxide and water from cryogenically produced nitrogen to below parts-per-billion (ppb) levels. The capability of the adsorbent decreases with time-on-stream or time-in-use. In order to rejuvenate the ability of the nickel-based catalytic adsorbent to remove the unwanted species, the adsorbent must be regenerated periodically. It is known to use hydrogen diluted with nitrogen to reactivate the adsorbent each time the capacity of the adsorbent to remove the unwanted species has reached the end of its cycle time. After the hydrogen reduction step, wherein the adsorbed unwanted species are removed from the catalytic adsorbent, a purge step is necessary to remove the residual hydrogen from the adsorbent bed. The use of a cycle of hydrogen reduction followed by a purging cycle creates an inefficiency in the production of UHP nitrogen because of the time required to purge the bed of hydrogen. In addition, the costs of operating such a regeneration scheme on a continuing basis are significant.